Fine particles having a diameter of about from several nanometers to 1 μm have been recently applied in various fields and attracted attention. The above-described fine particles include, for example, porous silica particles and zeolite particles to be used for an adsorbent or a catalyst, carbon black, metal oxide particles and inorganic compound particles to be used for a pigment, metal nanoparticles to be used for a conductive material, and silica particles to be used for a reinforcing agent of a resin. Thus, material and use of the fine particles are wide-ranging. Moreover, with regard to semiconductor nanoparticles, silica nanoparticles containing a fluorochrome, and so forth, an application as new labeling particles is expected particularly in a field of biotechnology. In addition, silica nanoparticles containing a dye with high concentration have a high molar extinction coefficient, and thus, an application thereof as further highly sensitive labeling particles is expected.
The above-described labeling particles can be used as a labeling reagent that can be used for detection, quantitative determination, dyeing or the like of a target molecule, by bonding a biomolecule (protein, nucleic acid or the like) having bonding capability with a specific target molecule on the surface of the particles.
Bonding of the labeling particles with the biomolecule is performed by physical adsorption, or also by allowing covalent bonding of both through a reactive functional group existing on the surface of the labeling particles. A stronger and more stable labeled biomolecule can be obtained by utilizing the covalent bond. As a method of introducing the reactive functional group onto the surface of the silica particles, a method is known in which organoalkoxysilane having a reactive functional group on the surface of core particles of silica is subjected to polycondensation in aqueous ammonia-containing solvent (for example, see Patent Literature 1).